1. Field of the Invention
The technical field relates to a method for manufacturing an ultra small particle, a positive electrode active material of a secondary battery using the method for manufacturing an ultra small particle and a method for manufacturing the same, and a secondary battery using the positive electrode active material and a method for manufacturing the same.
2. Description of the Related Art
The field of electronic devices having high portability such as laptop personal computers and cellular phones has progressed significantly. An example of power storage devices suitable for electronic devices having high portability is a lithium-ion secondary battery.
As a positive electrode active material of a lithium-ion secondary battery, a phosphate compound having an olivine structure and containing lithium (Li) and iron (Fe), manganese (Mn), cobalt (Co), or nickel (Ni), such as lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), or lithium nickel phosphate (LiNiPO4), has been known. High capacity can be safely achieved with LiFePO4 since FePO4 which is formed by completely extracting lithium from LiFePO4 is also stable. It is known that use of LiFePO4 whose particle size is reduced to approximately 50 nm as the positive electrode active material dramatically improves a charging and discharging rate (Non-Patent Document 1).
Further, it is known that LiFePO4 can be formed using a gel-like mixture of LiOH, Fe(NO3)3, H3PO4 and ascorbic acid (Non-Patent Document 2).
Meanwhile, a technique called a nanoimprinting method by which a fine pattern is formed using a mold (for example, Patent Document 1) is known. With the use of the nanoimprinting method, a hole having a diameter of 10 nm can be formed in PMMA (polymethylmethacrylate). Furthermore, a pattern with a hole having a diameter of 6 nm can be formed by a lift-off process (Non-Patent Documents 3 and 4).